This invention relates generally to carburetors and more particularly concerns a variable venturi carburetor.
Carburetors are used to atomize a liquid fuel and mix the atomized fuel with air for burning within the engine. A typical carburetor has a housing with an inlet, an outlet and a passageway connecting the inlet with the outlet. The passageway within the housing forms a venturi so that as the air passes through the venturi, a decrease in pressure occurs and the liquid fuel is withdrawn from a main nozzle disposed within the passageway just upstream of the throat of the venturi. The liquid fuel is atomized and mixed with the air as the air flow passes through the venturi. The mixture of atomized fuel and air is then carried into the engine for burning therein.
Among other variables, the degree of atomization and mixing of the fuel and air depends on the quantity of air passing through the venturi during a given time which depends on the engine speed and the throat size of the venturi. Thus, if the throat size of the venturi is fixed, there is only one engine speed where an ideal ratio of fuel-to-air occurs for any given engine. Thus, incomplete combustion of the fuel occurs at all other engine speeds for that particular engine. This incomplete combustion means that the engine is not running as efficiently as possible and pollutants are emitted from the exhaust of the engine.
A recent advance in carburetor design has been the development of a variable throat venturi within the passageway, which moves one wall relative to a fixed wall and regulates the flow of the liquid fuel into the venturi. An example of this design is disclosed in U.S. Pat. No. 3,896,195, wherein the regulation of the fuel into the venturi and the movement of the one side wall is controlled by a vacuum diaphragm operably connected to the venturi. The regulation of the fuel into the venturi takes place by a tapered valve element moveable within an opening provided in the non-moveable wall of the venturi and the valve element is mounted to the moveable wall and extends across the passageway. Thus, the change in the throat size of the venturi and the fuel flow is controlled by the drop in the vacuum, which depends on the speed of the engine.
Another recent advance in carburetor design has been the development of a variable throat venturi with both side walls of the passage being moveable relative to one another. An example of this design is disclosed in U.S. Pat. No. 3,949,025, wherein the passageway through the carburetor is defined by side walls which are pivotally mounted on the inlet side of the passageway and uses a cam member mounted on the outlet side of the passageway to move both walls together and apart simultaneously. The atomization of the fuel and movement of the air through the passageway is obtained by varying the area ratio between the throat and exit planes so that the air-to-fuel ratio is properly obtained as the engine idles.
Both of these designs have a problem in that turbulance develops as the air flows through the venturi which adversely effects atomization and mixing of the fuel. In the first design, this turbulance is created by the moveable valving element extending across the passageway. In the second design, it is believed the turbulance is created by the positioning of the pivotal axes of the side walls at the inlet and the cam at the outlet.
Further, the fuel introduced into the venturi of the latter carburetor design is not responsive to the velocity of the air passing through the venturi. This lack of regulation on the fuel flow permits the air-to-fuel ratio in this design to vary independently of the velocity of the air passing through the venturi which adversely affects the air-to-fuel ratio. If the regulation of the fuel flow was made similarly to the former design, the turbulance problem is made worst by disposing the valving element across the passageway.
An object of this invention is to provide a variable throat venturi carburetor having an aerodynamically designed passageway which eliminates the turbulance problems associated with the prior art carburetors.
Another object is to provide a variable throat venturi carburetor having side walls which simultaneously move toward and away from one another to increase the throat size as the engine speed increases and to decrease the throat size as the engine speed decreases to provide a constant air-to-fuel ratio for burning in an engine over a range of engine speeds.
Another object is to provide a variable throat venturi carburetor having side walls which are simultaneously moved toward and away from one another to increase the throat size as the engine speed increases and to decrease the throat size as the engine speed decreases and having a valving element provided in a fuel outlet leading from a fuel bowl to permit more fuel to flow as the engine speed increases and less fuel to flow as the engine speed decreases to provide a constant air-to-fuel ratio for burning in an engine over a range of engine speeds.
These and other objects are accomplished, in accordance with the invention, by a variable flow venturi carburetor which comprises a housing having an inlet, an outlet and a passageway therethrough connecting the inlet with the outlet, said passageway including generally parallel end walls and side walls having first portions which converge from the inlet to a rectangularly shaped throat intermediate the inlet and outlet and second portions which diverge from the throat to the outlet, and means for introducing fuel into the passageway upstream of the throat. In one novel aspect of this invention, wherein the first and second portions are plates, means are provided for simultaneously swinging the first and second plates about axes adjacent the inlet and outlet, respectively, so as to vary the size of the throat and means are also provided for controlling the side wall moving means in response to the speed of the engine by increasing the throat size as the engine speed increases and by decreasing the throat size as the engine speed decreases to provide a constant air-to-fuel ratio to an engine over a range of engine speeds. Another novel aspect of this invention uses means for simultaneously moving the side wall portions at the throat to vary the size of the throat and means are provided for controlling the side wall moving means in response to the speed of the engine by increasing the throat size as the engine speed increases and by decreasing the throat size as the engine speed decreases to provide a constant air-to-fuel ratio to an engine over a range of speeds. Another novel aspect of this invention, the carburetor includes a fuel bowl having an opening through which fuel is admitted, and a valving element which is shiftable between positions is provided for regulating the flow of fuel through the opening, means are provided for sensing a vacuum downstream of the throat in the passageway and means are provided responsive to the sensed vacuum for controlling a side wall moving means to increase the throat size as the engine speed increases and to decrease the throat size as the engine speed decreases and for regulating the valving element to permit more fuel to flow as the engine speed increases and less fuel to flow as the engine speed decreases to provide a constant air-to-fuel ratio to the engine over a range of engine speeds.